All present-day life arose from a single ancestor

Protein analysis rules out multiple sources

One isn’t such a lonely number. All life on Earth shares a single common ancestor, a new statistical analysis confirms.

The idea that life-forms share a common ancestor is “a central pillar of evolutionary theory,” says Douglas Theobald, a biochemist at Brandeis University in Waltham, Mass. “But recently there has been some mumbling, especially from microbiologists, that it may not be so cut-and-dried.”

Because microorganisms of different species often swap genes, some scientists have proposed that multiple primordial life forms could have tossed their genetic material into life’s

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